1. Field of the Invention
The present invention relates to a method for producing electrolytic ionic water and an apparatus for producing electrolytic ionic water, as well as a semiconductor manufacturing apparatus using this electrolytic ionic water for washing semiconductor substrates. In particular, this invention relates to a method for producing electrolytic ionic water by adjusting the pH.
2. Description of the Related Art
Electrolytic ionic water is widely used in various fields, in particular, in the manufacturing of semiconductor devices or liquid crystal displays. In particular, electrolytic ionic water obtained from electrolyzed pure water or ultra pure water is used during the manufacturing of semiconductors for washing and polishing.
Conventionally, fluorocarbon solvents, such as CCl.sub.3 F, have been used for washing semiconductor substrates during the manufacturing process. However, fluorine solvents may adversely affect the environment and sometimes are to be avoided. Thus, pure water or ultra pure water is often used as a safer solvent.
Pure water is high purity water having a specific resistance of 5 M.OMEGA.cm to 18 M.OMEGA.cm where impurities such as ions, fine grains, microorganisms, organic matters have been removed. Ultra pure water is extremely highly purified pure water, and has a specific resistance higher than 18 M.OMEGA.cm When pure water or ultrapure water (hereinafter, both referred to as pure water) is electrolyzed, the resulting product is electrolytic ionic water such as an anode ionic water, which is strongly oxidized (acidic water), and cathode ionic water, which is strongly basic or reduced (alkaline water).
A conventional electrolytic bath of an electrolytic ionic water generating apparatus has a cathode chamber and an anode chamber. A cathode is disposed in the cathode chamber and an anode is disposed in the anode chamber. The cathode and the anode, both electrodes, are made of metals such as platinum or titanium. In order to efficiently separate cathode ionic water generated in the cathode chamber and anode ionic water generated in the anode chamber, the cathode chamber and the anode chamber are partitioned by a porous membrane made of a ceramic material or a macromolecule. The cathode and the anode are connected to a direct current power source.
Diluted electrolytic solution of a particular pH value is prepared by diluting a supporting electrolyte or electrolytic solution, such as hydrochloric acid (HCl), nitric acid (HNO.sub.3), ammonium chloride (NH.sub.4 Cl), or ammonia (NH.sub.3), with pure water in an electrolytic bath. The solution is electrolyzed in the electrolytic bath by impressing a voltage from the power source. As noted, normally, the cathode ionic water generated in the cathode chamber is alkaline water and anode ionic water generated in the anode chamber is acidic water.
The cathode ionic water generated in the cathode chamber is supplied to an external apparatus through a cathode ionic water discharge line, while the anode ionic water generated in the anode chamber is supplied to an external apparatus through an anode ionic water discharge line.
When alkaline water is used, for example, in a polishing apparatus for manufacturing semiconductor devices, the cathode ionic water is supplied from the cathode chamber, and the acid water generated in the anode chamber is disposed from the anode ionic water discharge line. Similarly, when acid water is used in, for example, a polishing device, the anode ionic water is supplied from the anode chamber, and the alkaline ionic water generated in the cathode chamber is disposed of via the cathode ionic water discharge line. Thus, the electrolytic ionic water generating system can be applied to semiconductor manufacturing apparatuses such as polishing machines and washing wafers machines.
Under conventional methods, the pH value of electrolytic ionic water is regulated by controlling the concentration of the supporting electrolyte in the electrolyte solution or the amount of the current applied to the electrodes in the electrolytic bath. However, it is very difficult to regulate and maintain the desired pH values due to the heat generated by the electrolysis process. Further, a conventional electrolysis apparatus does not have a heat controller and typically can only operate at about room temperature.